This application claims the priority of Korean Patent Application No. 2003-6287, filed on Jan. 30, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a method and apparatus for image encoding and decoding, and more particularly, a method and apparatus for redundant image encoding and decoding of part of slices used for image encoding.
2. Description of the Related Art
A general image is compressed when redundant information is removed. When a moving image is compressed using this method, in general, temporal/spatial predictive encoding, transform/quantization encoding, and entropy encoding are sequentially performed.
When a compressed image is generated as a bitstream and is transmitted via a network, burst errors or packet loss errors occur. When these errors occur, a bitstream next to a portion in which errors occur cannot be decoded. In order to solve such a disadvantage, a conventional method by which a piece of image divided in units of a plurality of slices is encoded such that errors occur only in a corresponding slice, has been proposed. However, in the conventional method, when one slice is damaged by errors, picture quality of a corresponding image is damaged, and then, the errors are propagating throughout an image generated through spatial predictive encoding by referring to a damaged slice.
In order to prevent error propagation, a piece or part of an image in which temporal predictive encoding is not used is used periodically. In this method, error propagation can be prevented, but a bit number increases greatly, and thus, the method is used restrictively.
Thus, in the prior art, when an image is encoded in units of slices, the size of the slice is made small so that the slices are robust with an error. However, as the size of the slice becomes smaller, the number of bits needed to encode a slice header increases, and the number of bits to be encoded increases due to a compression loss which is generated because predictive encoding cannot be performed.
According to an MPEG-4 or a H.263 international standard, a slice is designated in units of bit numbers having a predetermined size or a series of macroblocks having a 16×16 size. In this case, when errors occur in one slice, the slice is damaged by the errors, and thus, a predetermined region of an image is damaged, and subjective picture quality is lowered. In order to solve this disadvantage, according to a recommendable proposal provided by a Joint Video Team (JVT) final committee, a flexible macroblock ordering (FMO) method is used. In this method, a slice is composed of arbitrary macroblocks. In this case, if errors occur in one slice, a macroblock included in the slice is not too much arranged in a particular area of an image, but is scattered over several regions of the image such that the damage of subjective picture quality is alleviated and an error concealment method using an undamaged peripheral block can be easily used.
Also, the recommendable proposal provided by the JVT final committee provides a redundant slice method by which the same one encoded slice is redundantly transmitted. However, this method can be effectively used when the size of the slice is small, but when the size of the slice is large, due to the increased number of bits of a redundantly-transmitted slice, an encoding efficiency is lowered.
Meanwhile, in the case of temporal predictive encoding used in a conventional image compression method, errors occurring in one point in time are continuously propagated over a next image. In order to prevent this error propagation, an intra-updating scheme for encoding sine part of an image without temporal predictive encoding is used. In this case, an encoding efficiency is lowered.
Also, in another conventional multiple encoding method, an image is encoded in units of bitstreams, and each bitstream is independently decoded, so as to improve error robustness. In this case, when each bitstream is independently decoded, an encoding efficiency is lowered, and the structure of a decoder becomes complicated so that each bitstream is independently decoded or decoded by adding to each other.
Further, in a conventional layer encoding method, information composed of a base layer and upper layers is encoded, and in a data division method, information composed of header information, motion information, and texture information is encoded. Even in this case, an additional encoding/decoding process is required, and important information needs to be separately protected so as to embody error robustness.